WARNING! When you master reset your phone, all the personal information stored on the device’s internal memory will be deleted, including media files, contacts, ringtones, downloaded content etc. Furthermore, all settings will be restored to factory values. However, data stored on the SD and SIM cards will not be removed.

NOTE: Before you factory reset your phone, you can visit this thread for instructions on how you can back up and restore data.

Master Reset via Settings:

Open the apps drawer

Go to “Settings”

Tap “Backup & reset” > “Factory data reset”

Tap “Reset phone” > “Erase everything”

After the reset is done, your phone will reboot

Master Reset Using Hardware Keys:

NOTE: In case you are unable to reset the phone via Settings, alternatively you can try resetting it using a combination of hardware buttons which give access to the Android System Recovery menu. To do this: